Current perpendicular to plane (CPP) giant magnetoresistance (GMR) based magnetic heads are considered as promising candidates for achieving a recording density of over 200 Gb/in2 [1-2]. In a CPP GMR head structure a bottom synthetic spin valve type film stack is employed for biasing reasons, and a CoFe/NiFe composite free layer is conventionally used following the experience with Current in Plane (CIP) GMR devices. It has already been demonstrated [3] that by laminating CoFe AP1 layers with thin Cu, CPP GMR performance can be improved. An example of a metallic CPP spin valve structure is:Seed/AFM/AP2/RU/[CoFeCu]/Cu30/[CoFe/NiFe]/cap
It has also been proposed [4] that CPP GMR performance will be further improved by a current confining path (CCP) in the Cu spacer achieved by providing a segregated metal path within an oxide. An example of a CCP-CPP spin valve structure is as follows:Seed/AFM/AP2/RU/[CoFeCu]/Cu/CCP-layer/Cu/[CoFe/NiFe]/cap
In a typical CPP spin valve structure of either case shown above, the AP1 or AP2 thickness is in the range of 20-50 Å, and the free layer thickness is in the range of 30-60 Å. For read head applications, the free layer is preferred to have a small coercivity (Hc) of less than 10 Oe and a low magnetostriction in the order of E-8 to low E-6 to reduce the stress-induced anisotropy.
For the past few years, there has been a lot of progress in the development of either metal CPP or CCP-CPP heads. However, for the metal CPP case, the CPP GMR ratio remains at a rather low value; for CCP-CPP schemes, since the current path is confined to Cu metal channels that are connected through an oxide matrix (AlOx, TiO2, or MgO layers) [5], the Cu purity is easily compromised during the insulator formation process, making the latter critical to ensuring a high MR ratio. A schematic cross-section of a CCP layer is shown in FIG. 1. Conduction through copper layer 11 can be seen to continue upward through copper filaments 12 which are surrounded by insulating oxide regions 13. The present invention discloses a method and structure in which no degradation of the Cu purity and the MR ratio will occur.    [1] M. Lederman et al U.S. Pat. No. 5,627,704    [2] J. W. Dykes et al U.S. Pat. No. 5,668,688    [3] Toshiba TMRC 2001    [4] M. Li et al, US 2006/0007605
A routine search of the prior art was performed with the following references of interest being found:
In U.S. Pat. No. 7,005,691, Odagawa et al. show a non-magnetic copper film and an insulating film comprising an oxide, carbide, or nitride. In U.S. Patent Application 2005/0157433, Kamiguchi et al. show a resistance regulating layer in a copper non-magnetic layer comprising an oxide, nitride, fluoride, carbide, or boride.
U.S. Patent Application 2005/0094322 (Fukuzawa et al.) teaches plasma oxidation or nitridation of a metal non-magnetic layer. U.S. Patent Application 2005/0002126 (Fujiwara et al) says “instead of oxidation, nitridation may work if materials with different susceptibility to nitridation are chosen.” However, this notion is not pursued any further, no detailed process or explanation being given. Additionally, the basic process underlying this invention is significantly different from the present invention. For example, the locations of the CCP layers and how to form them.